How can I as a guy practice to sing high notes? Like. I'm trying to cover some Good Charlotte songs, but when I go to hit the high notes, I don't quite get there. I do support loads from the diaphragm, and sing loud and clear. Is it all about practice?

Some of it's just practice, it may just be out of your range though. But from my personal experience as someone who was able to "crack" some higher notes in the early stages, after months I was able to hit those cracked notes from just singing and practicing. You can extend your range slightly.

Other wise you may want to look into developing your mixed voice to help with the highs.

The one thing that really helped me out that my teacher told me, and it's so simple. Just think "O" whenever you sing. You want that open feeling.

Don't "reach" for the notes. Pretend they're right in front of your nose and let the note resonate through your head cavities. The feeling is if you hum and push it forward (leave as much of the throat as feasibly possible out of it) and you feel your nose and cheeks kind of vibrate and tingle. But we used a lot of humming exercises, just simple scales and arpeggios to work on that.

when singing high notes, there's 2 main elements. One element is having a balance between air applied and the closure of your head voice pitches. You don't want to apply a lot of air for only a little bit of closure.

and the second element is having a very small mouth opening to make use of your pharyngeal and head voice. The wider your mouth, the more you tend to use chest voice, which is bad. All of your high notes are always sung with a really small mouth position.

see if you can hit the notes when you sing softly and relax. do not push.
if you can do that, then to raise the volume and still keep your voice sounding fat, drop your throat down as if you are doing the "yogi bear" voice (where is the pic-a-nic basket booboo?) and open your throat like you are yawning.